Wood composites such as fibre board and particle board are made by binding the material (e.g. wood fibres or wood particles) with a suitable binder and pressing, usually with heating. Conventional chemical binders for this purpose are e.g. urea-formaldehyde resin and phenol-formaldehyde resin.
Binders made from enzymatically treated lignin are also known. Thus, it has been suggested to use a binder made from peroxidase treated lignin (vide e.g. U.S. Pat. No. 4,432,921), but the use of a peroxidase has not previously been demonstrated.
For wood composites, e.g. for use in construction, a high physical strength is generally important. In order to obtain high physical strength it is essential that an optimal polymerization/modification takes place during binding of the material.
As a liquid binder material is believed to be a prerequisite for optimal polymerization, enzymatic polymerization processes, due to the reaction pH of the enzymes hitherto employed, optionally involve the addition of organic solvents in order to solubilize lignin (vide e.g. EP Patent Application No. 354,485).
Another way of improving the strength of the composite board involves addition of chemical polymerization agents, e.g. polydiphenylmethyldiisocyanate (PMDI), (vide e.g. EP Patent Specification No. 275,544).